Can't apply Material to Part of Model
You need to switch to Cycles Render. If you don't you may not be able to see some stuff you have done.
Switch the viewport shading not to Texture but to Material that way you can see the stuff you have done.
In Edit Mode select what/where you want to color using different kinds of selecting (either use the looping methods (&#9096; Ctrl LMBand hold and drag, or hold B LMB hold and drag) or select manually by  RMB clicking and holding &#8679; Shift or &#9096; Ctrl), then create a Material and click assign.


Make sure you name the Materials so you can tell them apart later.